//===================================================================================
// Microsoft patterns & practices
// Composite Application Guidance for Windows Presentation Foundation and Silverlight
//===================================================================================
// Copyright (c) Microsoft Corporation.  All rights reserved.
// THIS CODE AND INFORMATION IS PROVIDED "AS IS" WITHOUT WARRANTY
// OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT
// LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
// FITNESS FOR A PARTICULAR PURPOSE.
//===================================================================================
// The example companies, organizations, products, domain names,
// e-mail addresses, logos, people, places, and events depicted
// herein are fictitious.  No association with any real company,
// organization, product, domain name, email address, logo, person,
// places, or events is intended or should be inferred.
//===================================================================================
using System;
using Microsoft.Practices.Prism.Properties;
using Windows.UI.Xaml;

namespace Microsoft.Practices.Prism.Regions.Behaviors
{
	/// <summary>
	/// Behavior that synchronizes the <see cref="IRegion.Context"/> property of a <see cref="IRegion"/> with 
	/// the control that hosts the Region. It does this by setting the <see cref="RegionManager.RegionContextProperty"/> 
	/// Dependency Property on the host control.
	/// 
	/// This behavior allows the usage of two way databinding of the RegionContext from XAML. 
	/// </summary>
	public class SyncRegionContextWithHostBehavior : RegionBehavior, IHostAwareRegionBehavior
	{
		private const string RegionContextPropertyName = "Context";
		private DependencyObject hostControl;

		/// <summary>
		/// Name that identifies the SyncRegionContextWithHostBehavior behavior in a collection of RegionsBehaviors. 
		/// </summary>
		public static readonly string BehaviorKey = "SyncRegionContextWithHost";

		private ObservableObject<object> HostControlRegionContext
		{
			get
			{
				return RegionContext.GetObservableContext(this.hostControl);
			}
		}

		/// <summary>
		/// Gets or sets the <see cref="DependencyObject"/> that the <see cref="IRegion"/> is attached to.
		/// </summary>
		/// <value>
		/// A <see cref="DependencyObject"/> that the <see cref="IRegion"/> is attached to.
		/// This is usually a <see cref="FrameworkElement"/> that is part of the tree.
		/// </value>
		public DependencyObject HostControl
		{
			get
			{
				return hostControl;
			}
			set
			{
				if (IsAttached)
				{
					throw new InvalidOperationException(Resources.HostControlCannotBeSetAfterAttach);
				}
				this.hostControl = value;
			}
		}

		/// <summary>
		/// Override this method to perform the logic after the behavior has been attached.
		/// </summary>
		protected override void OnAttach()
		{
			if (this.HostControl != null)
			{
				// Sync values initially. 
				SynchronizeRegionContext();

				// Now register for events to keep them in sync
				this.HostControlRegionContext.PropertyChanged += this.RegionContextObservableObject_PropertyChanged;
				this.Region.PropertyChanged += this.Region_PropertyChanged;
			}
		}

		void Region_PropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
		{
			if (e.PropertyName == RegionContextPropertyName)
			{
				if (RegionManager.GetRegionContext(this.HostControl) != this.Region.Context)
				{
					// Setting this Dependency Property will automatically also change the HostControlRegionContext.Value
					// (see RegionManager.OnRegionContextChanged())
					RegionManager.SetRegionContext(this.hostControl, this.Region.Context);
				}
			}
		}

		void RegionContextObservableObject_PropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
		{
			if (e.PropertyName == "Value")
			{
				SynchronizeRegionContext();
			}
		}

		private void SynchronizeRegionContext()
		{
			// Forward this value to the Region
			if (this.Region.Context != this.HostControlRegionContext.Value)
			{
				this.Region.Context = this.HostControlRegionContext.Value;
			}

			// Also make sure the region's DependencyProperty was changed (this can occur if the value
			// was changed only on the HostControlRegionContext)
			if (RegionManager.GetRegionContext(this.HostControl) != this.HostControlRegionContext.Value)
			{
				RegionManager.SetRegionContext(this.HostControl, this.HostControlRegionContext.Value);
			}
		}
	}
}